It's been about a week now running my Hyper-V hosts on the 7.8.50.0 version of the driver, and it does seem like the issue is gone. Funny that the release notes didn't seem to say anything related to this problem.
The notes for 7.8.50.0 say this:
Fixes
- This driver corrects an issue that could result in halted traffic when configuring jumbo frame size to 9000.
- This driver corrects an issue that could result in a Windows Stop Error (BSOD) when a large number of ports are repeatedly disabled.
As a side note, on my Hyper-V hosts, these are Server 2012 systems and I use the native Microsoft teaming service, with all of the NIC ports set to Hyper-V Port load balancing (not aggregated or anything since they're connected to redundant switches on separate power feeds). I don't know if that would make a difference or not.
We're not using jumbo frames, so that wouldn't apply. I guess it's just some undocumented thing they slipped in or fixed silently.